Nowadays, increasingly strict requirements apply to automatic transmissions with electro-hydraulic control systems in relation to reducing fuel consumption and exhaust emissions, while at the same time maintaining spontaneity and comfort. In addition, the manufacturing and assembly costs of automatic transmissions should be reduced. In this respect the pump systems needed for the operation of automatic transmissions are an important factor in relation to fuel consumption and exhaust emissions; furthermore, the pump systems known from the prior art have disadvantages relating to structural space occupation, and electrically powered pumps burden the on-board voltage of the vehicle to a disadvantageous extent.
From the prior art, transmission oil pumps are known, which are driven by the vehicle's internal combustion engine and/or by an electric machine of the vehicle. In addition pump systems are known, which have two pumps driven by the internal combustion engine or an electric machine. Furthermore, displacement pumps, two- or multi-flow pump designs and pumps combined with a pressure reservoir are known.
From DE 19705957 C1 by the present applicant a mechanically driven transmission oil pump arranged with its axis parallel to the transmission input shaft is known, between which and a drive element is arranged a pump clutch formed as a liquid crystal clutch with a liquid crystal clutch control system, whose controllable slip makes it possible to vary the pump driving speed.
From DE 3812412 A1 a pump drive system is known, with at least one constant pump and a planetary transmission with variable transmission ratio arranged between the pump and two working machines that drive the pump, such that the pump is connected to the drive output side of the planetary transmission and the other two shafts of the planetary transmission are connected to a first working machine, in the form of an internal combustion engine, and to a second working machine, in the form of an electric motor or a second pump, in such manner that by regulating the power of the two working machines the pump speed of the main pump can be varied according to need.
In this case, owing to the power branching in the planetary transmission there is at all times a speed-related coupling between all the components, so that the electrical drive branch cannot drive the pump independently of the mechanical drive branch; accordingly, the planetary transmission does not work as a two-gear transmission.
Moreover, from U.S. Pat. No. 5,669,842 an electro-mechanical hybrid drive is known, which comprises an electrical energy and storage source, a first motor/generator, a second motor/generator, control means for connecting the energy and storage source selectively to the first and the second motor/generators in order to control their respective operation, an internal combustion engine with an idling speed, a planetary gear assembly with a first element in driving connection with the first motor/generator, and a second element in driving connection with the second motor/generator, and a hydraulically actuated clutch which can be brought selectively into engagement in order to connect the drive machine with a third planetary transmission element of the planetary gear assembly. In this case it is provided that the third element of the planetary gear assembly is in driving connection with a number of driveshafts for auxiliary devices, one of which is in driving connection with a hydraulic energy source, so that the first and second motor/generators can be operated by the planetary gear assembly to actuate the hydraulic energy source and to control the speeds of the first and second element and thereby to rotate the third element of the planetary gear assembly at a speed which is proportional to the idling speed when the clutch is disengaged, so as to establish selective engagement of the clutch at a speed synchronous with the idling speed.
In the context of DE 10311270 A1 a hybrid drive with a pump is known, which is driven by an electric motor via a transmission with constant transmission ratio.
Furthermore, from DE 102007039083 A1 by the present applicant an axis-parallel transmission oil pump with a planetary transmission connected upstream in the force flow is known, the carrier of the planetary transmission being in active connection with the converter pump impeller or with the motor shaft and its ring gear with the converter turbine wheel or the transmission input shaft, such that a freewheel that can freely roll during thrust operation is provided between the ring gear and the transmission housing. In this case the drive input speed of the pump is adjusted as a function of a pump speed of the torque converter, which corresponds to the speed of the vehicle's drive aggregate, and as a function of a turbine speed of the torque converter, in such manner that when the pump speed of the torque converter is higher than its turbine speed, the pump is driven at a drive speed higher than the speed of the drive aggregate, and when the turbine speed of the torque converter approaches its pump speed, the excess of the pump's drive speed compared with the speed of the drive aggregate is reduced.